In industrial sewing machines of the lock stitch type which require bobbins and which operate at high speeds consuming a large amount of thread on the bobbin, the problem presented by changing bobbins is a serious economic one. The sewing machine is normally only one part of a sequence of machinery which for many operations is extremely expensive, and stoppage of the sewing machine and hence interruption of the whole operation in order to change bobbins represents a serious cost for the down time during bobbin change.
Originally sewing machine bobbins were changed by hand, which is a slow operation and requires both considerable additional labor and cost for the down time of an expensive organization of machinery.
In the past automatic bobbin changers for industrial sewing machines have been built and used. These changers grasp an empty bobbin with a hook, requiring several elements for actuation. The hook first catches the lid of the bobbin case and opens it and, finally as it retracts further, pulls the empty bobbin and case out, which then drop into a suitable container. The mechanism, including the hook, is usually mounted on a cross slide and can be moved to a second position aligned with a magazine of full bobbins and cases. In this position it is actually removing a full bobbin and case to a suitable carrier housing or other element on the slide. The slide then moves back to its first position and the hook moves forward, pressing the full bobbin and case onto the conventional latch, usually a pin, which holds a full bobbin in the sewing machine during operation. Since the hook is pushing, it does not open the lid and is then retracted onto the slide, permitting the cycle to be repeated when the conventional sensor on the sewing machine indicates that the replaced bobbin is practicallly empty. Actuation of the elements moving the hook and of the slide may be pneumatic or hydraulic or may be electrical.
A typical illustration of the automatic bobbin changer described above is to be found in the Schiffmacher and Roman U.S Pat. 3,376,838, Apr. 9, 1968. It will be noted that there is only a single mechanism including the hook and that the cross slide is provided with a suitable carrier housing or other elements for carrying a full bobbin and case from a magazine on the next cycle.
While automatic bobbin changers greatly speeded up bobbin changing as compared to manual changing and are quite generally used on industrial sewing machines, this saving in time is achieved only at the cost of a serious problem. The hook which has been described can jam the case latch, which of course then requires stopping the changing mechanism and freeing the jammed bobbin case from the hook manually. This operation takes some time, and in the meantime the sewing machine and any related machinery which is synchronized with the sewing operation stops. This results in down time with markedly increased costs. The automatic bobbin changing machines which have been used and which are described above do not jam every time they change bobbins but this happens sufficiently frequently to present a serious problem. In other words, the automatic bobbin changers which have been used in the past are not inoperative when a bobbin case does not jam as the lid is grasped by the hook, but the problem still remains and leaves room for improvement. It is with an improved automatic bobbin changer of quite different structure, which cannot jam, that the present invention deals.